Autumn Institute II: Testing the Standard Model at low and high energies

Tuesday 28 Nov 2017, 10:00 → 17:30 Europe/Rome

Aula Seminari (Laboratori Nazionali di Frascati (Rome), Italy)

Gennaro Corcella (LNF)

Aim of the workshop:
The Autumn Institute II will gather theorists and experimentalists, working mostly in the Rome area and at CERN in the field of collider physics. In an informal environment, we shall investigate a few selected topics on possible tests of the Standard Model at low and high energies. In particular, we will discuss open issues in the dark sectors (dark photons and dark matter), the prospects for Lepton Flavour Violation in the Mu2e experiment, tests of discrete symmetries, such as CP and CPT at KLOE, as well as the latest observations of top-pair production in association with Higgs bosons at the LHC.
Speakers:
Barbara Mele (INFN Roma)
"Searching for a massless dark photon"
Stefano Miscetti (INFN LNF)
"Mu2e: The search for muon-to-electron conversion at Fermilab"
Doojin Kim (CERN)
"Searches for `Relativistic' Inelastic Dark Matter"
Valentina Vecchio (Università di Roma 3)
"Evidence for ttH production with the ATLAS detector"
Antonio Di Domenico (Università di Roma `La Sapienza')
"Test of discrete symmetries with neutral kaons at KLOE-2"

1 Searching for a massless dark photon

If dark photons are massless, they couple to standard-model particles only via higher dimensional operators, while the kinetic mixing with photons, which motivates most of the current experimental searches, is absent. We discuss a few processes that could be sensitive to the production of massless dark photons at present and future colliders, and at fixed-target experiments.

Speaker: Barbara Mele (ROMA1)

Slides Mele_LNF_2017.pdf

2 Mu2e: The search for muon-to-electron conversion at Fermilab

The Mu2e experiment aims to measure the charged-lepton flavour violating (CLFV) neutrino-less conversion of a negative muon into an electron in the field of a nucleus. The conversion process results in a monochromatic electron with an energy slightly below the muon rest mass (104.97 MeV). Goal of the experiment is to improve of four orders of magnitude the previous measurement with similar technique and reach of a SES (single event sensitivity) of 3 x 10^{-17} on the conversion rate with respect to the muon capture rate. Although the SM is well tested in many regimes, it appears likely to be incomplete. In many of the Beyond the Standard Model (BSM) scenarios, rates for CLFV processes are within the reach of the next generation of experiments. In particular, if SUSY particles have masses and couplings within the discovery reach of the LHC, CLFV rates will be observable. On the contrary, many CLFV searches have a sensitivity to new physics that exceeds the LHC reach up to new mass scale of O(10^4) TeV. In this contest indirected measurements of CLFV will be crucial evidence of new physics. Complementarity of Muon to conversion experiments and MEG upgrade is relevant in this respect. The experiment goal is obtained with a very intense pulsed negative muon beam sent to an Aluminium target for a total number of 10^{18} stopped muons in three years of running. Production and transport of the muons is done with a complicated and sophisticated magnetic systems composed by a production, a transport and a detector solenoid. The magnetic systems allows to bring this very intense beam to target with a low request on power. Description and status of the magnetic system will be reported. The improvement with respect to previous conversion experiments is based on four elements: the muon intensity, the beam structure layout, the extinction of out of time particles and the precise electron identification in the detector solenoid. The conversion electron will be reconstructed and separated by the Decay in Orbit (DIO) background by a very high resolution (180 keV) tracking system based on straw technology. The crystal calorimeter system will confirm that the candidates are indeed electrons by performing a powerful mu/e rejection while granting a tracking independent HLT filter. A Cosmic Ray Veto system surrounds the detector solenoid and contributes to make the cosmic based background negligible. The Mu2e experiment is under design and construction at the Muon Campus of Fermilab and has obtained CD-3 approval in July 2016. In the current schedule, the experiment start is foreseen for the end of 2020 with 3 years of running from 2021 to 2023.

Speaker: Stefano Miscetti (LNF)

Slides Mu2e-theory-seminar-v1.pdf Mu2e-theory-seminar-v1_.pptx

12:00 Lunch Break

3 Searches for `Relativistic' Inelastic Dark Matter

I will propose a new dark matter direct detection strategy under non-minimal dark sector models. The main idea is to look for relativistic and inelastic scattering signatures of dark matter. An incoming boosted dark matter particle scatters off to a heavier unstable (dark-sector) state (if kinematically allowed) which subsequently decays back into dark matter along with lighter states including visible Standard Model particles. The expected signature is an energetic recoil of the target particle associated with the secondary decay product(s) from the heavier unstable state, which is quite unique and distinguishable from potential backgrounds. I will discuss some interesting phenomenology at several benchmark detectors/experiments.

Speaker: Dr Doojin Kim (CERN)

Slides Presentation_INFN_DoojinKim.pdf

4 Evidence for ttH production with the ATLAS detector

The current status on the search for the production of the Higgs boson with a top quark pair (ttH) using proton-proton collision data at a center-of-mass energy of 13 TeV is reported. The ttH production allows to constrain the top Yukawa coupling, which is a key parameter of the Standard Model and its direct measurement through the ttH production mode is one of the most challenging physics program at LHC. The ATLAS collaboration recently claimed for the evidence of this process after the explorative analysis of the full 2015 and 2016 dataset. The details of the analysis that led to the evidence, together with the state of the art of the CMS collaboration ttH search analysis, will be reviewed.

Speaker: Valentina Vecchio (ROMA3)

Slides ttH_VVecchio.pdf

5 Test of discrete symmetries with neutral kaons at KLOE-2

A direct test of the T, CP and CPT symmetries in the neutral kaon system can be performed comparing a transition process i → f to its symmetry conjugated one. The exchange of in and out states required for genuine tests involving the time-reversal T can be performed exploiting the entanglement of the kaon pair produced at a φ-factory. In particular using this method it would be possible to perform a very clean and fully robust CPT test, which might shed light on possible new CPT violating mechanisms. The KLOE-2 experiment at the INFN Laboratori Nazionali di Frascati (LNF) is currently taking data at the e+e- DAFNE collider, the Frascati φ-factory. An integrated luminosity of 4.5/fb has been already collected by KLOE-2, and at least 5/fb are expected by Spring 2018. The implementation of the CPT test in transitions at KLOE-2 will be discussed and recent KLOE results on related CP/CPT tests will be presented.

Speaker: Antonio Di Domenico (ROMA1)

Slides didomenico_LNF_autumn_inst_5.pdf